ACDs utilizing an electromagnetic lock for securing doors, gates, or other types of closures are well known. In a typical installation of an electromagnetic lock, a magnetically-susceptible keeper plate is mounted on a door, and an electromagnet is mounted on a door frame. When the electromagnet is energized and is in contact with the keeper plate with the door in a closed position, the keeper plate becomes an armature for the electromagnet, thus providing a mechanism for locking the door to the frame.
Currently available electromagnetic locks have some undesirable physical attributes. For example, these systems physically protrude into the door opening, thereby creating undesirable safety, convenience and aesthetic issues. Furthermore, the configuration and structure of existing electromagnetic locks do not stand-up well to door slams, which create an impact between the electromagnet that is attached to the frame and the keeper plate that is attached to the door.
Installers of electromagnetic locks or other types of access control components are frequently confronted with the lack of standardization in the industry relative to supply voltages. Some ACDs anticipate and provide for operation at 12 or 24 volts DC and others anticipate and provide for AC voltage operation. As such, supply voltages ranging from 12 to 40 volts DC or 12 to 28 volts AC may be encountered at a particular location. An installer would therefore need to match the device to the available voltage. This has traditionally meant that the installer needed to stock a supply of different locking devices that can accommodate various voltages or in some cases make complicated on-site adjustments. Adjustments create the opportunity for errors in installation or configuration, and introduce delays in the installation process. Some attempts have been made in the industry to address some of these issues or drawbacks. For example in an environment that presents 12 or 24 volts DC, one approach to overcome the previously described issue has been to utilize or provide a system having two identical coils which can be run in series or parallel, to thereby handle one supply voltage or the other for powering the magnetic coil lock. Heretofore, such systems have utilized a double pole double throw (DPDT) switch, which the installer must then set appropriately at the time of installation. Nevertheless, prior attempts to accomplish voltage selection in the field necessitated allowance for a voltage drop across the input diode. This drop resulted in a reduced holding force for the electromagnet.
Another issue that is faced with traditional installation of an electromagnetic lock is in the area of passive motion detection for the passive release of an egress door. Passive motion detectors are commonly installed as a separate unit relative to the electromagnetic lock. A common problem that exists in the field with these systems is where the separate passive motion detector such as a Passive Infrared Reader (PIR) is not properly installed and/or adjusted properly to the door with respect to the location of the electromagnetic lock. Normally, the electromechanical lock is located with respect to the door hardware. If the PIR is physically apart from the electromagnetic lock, it may not be in the proper position to detect motion near the door hardware. However, when it is located within the electromagnetic lock, it can be accurately adjusted to detect motion in a location relevant to the door hardware. If the PIR is adjusted to sense motion too far out from the door, it may not detect a person close to the door that is attempting to exit the door, thereby causing the electromagnetic lock not to unlock thus creating a safety hazard for the person. Another problem exists if the egress door is located along a hallway and the PIR's field of view is too large. This overly large view allows the PIR to not only detect those persons wishing to exit the door, but also to detect people walking down the hallway, thereby resulting in the electromagnetic lock inadvertently unlocking and leaving the door unlocked and unsecured for short periods of time. This situation also creates an unsafe condition by potentially allowing an intruder the ability to enter the building.
Another problem concerning the use of PIR motion detectors in association with doors is the sensitivity of the unit with respect to background conditions. Different surfaces reflect IR differently and impact the ambient lighting environment, i.e. an individual's IR signature may be different if the floor is a polished concrete versus a colored Berber carpet. The same can be said with regard to fluorescent lighting vs. incandescent lighting. Also, building automation systems may reduce ambient lighting in off hours which would have an impact where the IR sensitivity would need to be adjusted to remain consistent.
What is needed is a robust and efficient electromagnetic lock for access control systems that can be universally implemented without the drawbacks and deficiencies described above. What is further needed is an ACD that includes a low profile electromagnetic lock that supports modern accessories such as, for example, a Closed Circuit Television (CCTV) camera, Charge-Coupled Device Television (CCD-TV) camera, passive motion detection, digital notification display, automatic source voltage selection, door or lock status indicators. What is still further needed is a device that is easy to install accurately, while avoiding the short comings of current systems is desired. The present invention fills these needs as well as other needs.